Continuous production of molded plastic containers

ABSTRACT

A system for making plastic containers includes a source for providing a continuous stream of molten plastic, and a cutter for severing a continuing series of individual mold charges from the continuous molten plastic stream. A compression molder includes a plurality of compression molds arranged in a continuing series for receiving the mold charges in sequence and compression molding the mold charges into a continuing series of individual plastic container preforms. A blow molder includes a plurality of blow molds arranged in a continuing series for receiving the individual plastic container preforms in sequence and blow molding the preforms into a continuing series of plastic containers. A common drive coordinates continuous and synchronous operation of the molten plastic source, the cutter, the compression molder and the blow molder to provide the continuing series of plastic containers from the continuous stream of molten plastic.

The present invention is directed to blow molding plastic containers,and more particularly to a system and method for continuous productionof plastic containers from polymer in melt phase.

BACKGROUND AND SUMMARY OF THE INVENTION

Preforms for blow molding plastic containers typically are produced inbatch processes, in which one or more solid phase polymers such aspolyethylene terephthalate (PET) are melted and injected into preformmolds. The injection molded preforms are blow molded to form plasticcontainers, usually at some later time. A general object of the presentinvention is to provide a system and method for continuous production ofblow molded plastic containers from molten polymer.

A system for making plastic containers in accordance with one presentlypreferred aspect of the invention includes a source for providing acontinuous stream of molten plastic, and a cutter for severing acontinuing series of individual mold charges from the continuous moltenplastic stream. A compression molder includes a plurality of compressionmolds arranged in a continuing series for receiving the mold charges insequence and compression molding the mold charges into a continuingseries of individual plastic container preforms. A blow molder includesa plurality of blow molds arranged in a continuing series for receivingthe individual plastic container preforms in sequence and blow moldingthe preforms into a continuing series of plastic containers. A commondrive coordinates continuous and synchronous operation of the moltenplastic source, the cutter, the compression molder and the blow molderto provide the continuing series of plastic containers from thecontinuous stream of molten plastic.

A method of making plastic containers in accordance with another aspectof the present invention includes providing a continuous stream ofmolten plastic, cutting the continuous stream into individual moldcharges, and transferring the mold charges in sequence into a continuingseries of compression molds. A continuing series of plastic containerpreforms are compression molded in the compression molds, and aretransferred in sequence to a continuing series of blow molds. Acontinuing series of plastic containers is formed in the blow molds andremoved in sequence. The step of transferring the preforms to the blowmolds preferably includes conditioning the preforms preparatory to blowmolding.

A system for making plastic containers in accordance with a thirdpresently preferred aspect of the invention includes a source forproviding a continuous stream of molten plastic, and a compression orinjection molder for molding a continuing series of individual plasticcontainer preforms. A blow molder includes a plurality of blow moldsarranged in a continuing series for receiving the individual plasticcontainer preforms in sequence and blow molding the preforms into acontinuing series of plastic containers. A common drive coordinatescontinuous and synchronous operation of the molten plastic source, thepreform molder and the blow molder to provide the continuing series ofplastic containers from the continuous stream of molten plastic.

BRIEF DESCRIPTION OF THE DRAWING

The invention, together with additional objects, features, advantagesand aspects thereof, will be best understood from the followingdescription, the appended claim and the accompanying drawing, which is aschematic diagram of a system for making plastic containers inaccordance with one presently preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The drawing illustrates a system 10 for making plastic containers inaccordance with a presently preferred embodiment of the invention. Anextruder 12 receives one or more plastic resin materials from associatedhoppers 14. Extruder 12 is driven by a motor 16 to provide a continuousstream of plastic resin material in melt phase to an extrusion nozzle18. The plastic resin material may comprise molten PET, for example, tofabricate containers of monolayer PET construction. As an alternative,multiple extruders 12 can feed associated streams of molten plasticmaterial to nozzle 18, with nozzle 18 being constructed to provide acontinuous stream of layered resin material for fabrication ofmultilayer containers. Such containers may have inner and outer surfacelayers of PET construction, for example, and one or more intermediatelayers of barrier material, such as ethylene vinyl alcohol (EVOH) ornylon, to retard migration of gas, water vapor and/or flavorants throughthe container wall. As another alternative, extruder 12 can be replacedby a reactor within which the resin material, such as PET, is producedby melt phase polymerization.

The continuous stream of molten plastic resin is fed to a pellet cutter20 and a transfer mechanism 22 for severing a continuing series ofindividual mold charges from the continuous stream of plastic resin, andtransferring the mold charges to individual molds 26 of a compressionmolder 24. Compression molder 24 preferably includes a plurality ofcompression molds 26 arranged in a continuous series for receiving themold charge pellets in sequence and compression molding the mold chargepellets into a continuing series of individual plastic containerpreforms. The compression molds 26 preferably are carried by a rotatableturret 28, which is driven in synchronism with rotation of cutter 20 andtransfer mechanism 22. Compression molder 24, transfer mechanism 22 andcutter 20 may be as disclosed in U.S. Pat. No. 5,866,177 or U.S. Pat.No. 6,349,838, for example, the disclosures of which are incorporatedherein by reference.

After the preforms have been compression molded and cooled sufficientlyto retain their shape, the preforms are individually removed from molds26 and transferred by wheels or other suitable transfer devices 30, 32to a conditioning stage 34. At conditioning stage 34, the preforms arefed in a loop 36 around a wheel 38, and then back to a preform transferwheel 40. During travel in loop 36, the preforms are allowed to coolfrom the temperature at which they exit compression molder 24 to atemperature suitable for blow molding. For example, PET preforms may bewithdrawn from compression molder 24 at a temperature of about 280 to300° F., and allowed to cool at conditioning stage 34 to a temperatureof 210 to 220° F. suitable for blow molding. Conditioning stage 34 mayalso include selective heating to obtain a temperature profile in thepreform suitable for blow molding, and may include crystallization ofportions of the preform, such as the preform finish. Conditioning stage34 may comprise a rotating wheel or turret, or an extended conveyor loopalong which the preforms are carried.

After preform conditioning at stage 34, the preforms are transferred toa blow molder 42 by the wheel, turret or other suitable transfer device40. Blow molder 42 includes a continuing series of blow molds 44 mountedon a turret or the like 46 for receiving the preforms in sequence, andblow molding the preforms into containers of desired geometry.(Reference to compression molding or blow molding preforms or containers“in sequence” does not mean that the preforms or containers are formedone at a time. Indeed, compression molder 24 and/or blow molder 42preferably includes facility for compression molding or blow moldingmultiple preforms and containers at each mold stage.) Blow molder 42 maybe of the type disclosed in U.S. Pat. Nos. 5,683,729, 5,863,571 and6,168,749, the disclosures of which are incorporated herein byreference. Following blow molding, the containers are transferred by awheel, turret or other suitable device 48 to a conveyor 50 for movingthe containers to subsequent manufacturing stages, such as labeling(decorating), filling, capping and crating stages. As an alternative,the subsequent stages may be linked directly to blow molder 42 to forman integrated sequential system.

Additional stages may be added for operating on the finish of thepreform or container. For example, the finish can be crystallized, asillustrated for example in U.S. application Ser. No. 10/122,901 filedApr. 12, 2002. As another example, finish rings can be added to thefinish neck prior to or subsequent to blow molding, as disclosed forexample in U.S. application Ser. Nos. 10/375,737, 10/403,415,10/375,736, 10/351,671 and 10/375,758. Other forms of finishmanipulation could be implemented.

A common or integrated drive/control mechanism 52 is connected to thedrive 16 of extruder 12, the drive of cutter 20 and transfer wheel 22,the drive of compression molder turret 28, the drive of conditioningstage 34, the drive of blow molder turret 46, to the drive of conveyor50 and the drives of the various transfer devices to operate and controlthese drive mechanisms continuously and in synchronism for continuousproduction of containers at the output of blow molder 42 from acontinuous stream of molten plastic at the output of extruder 12.Drive/control mechanism 52 may comprise servo control electronics forsynchronizing operation of servo motors connected to extruder 12,compression molder 28, conditioning stage 34, blow molder 42 andconveyor 50. As an alternative, drive/control 52 may comprise a singlemotor that is connected by suitable drive mechanisms, such as belts,gears or chains, to the operating mechanisms of the extruder,compression molder, conditioner, blow molder and conveyor. In eitherevent, the extruder, preform compression molder, preform conditioner,container blow molder and conveyor are operated continuously andsynchronized with each other for continuous production of containersfrom the molten output of the extruder.

There have thus been disclosed a system and method for making plasticcontainers that fully satisfy all of the objects and aims previously setforth. The system and method of the invention possess a number ofadvantages over the prior art, including but not limited to: (1) Reducedintrinsic viscosity (IV) loss in the preform, yielding better partquality and the opportunity to use lower cost material. (2) Reducedenergy required because the preform does not need to be reheated fromroom temperature prior to blow molding. (3) Reduced cost of customizingthe system to permit addition of modules for finish manipulation, finishcrystallization, container decoration, filling and capping, etc. Theinvention has been described in conjunction with one presently preferredembodiment, and a number of modifications and variations have beendiscussed. Other modifications and variations will readily suggestthemselves to persons of ordinary skill in the art. The invention isintended to embrace all such modifications and variations as fall withinthe spirit and broad scope of the appended claims.

1. A system for making plastic containers, which includes: a source forproviding a continuous stream of molten plastic, a cutter coupled tosaid source for severing a continuing series of individual mold chargesfrom said continuous stream, a compression molder including a pluralityof compression molds arranged in a continuous series for receiving saidmold charges in sequence and compression molding said mold charges intoa continuing series of individual plastic container preforms, a blowmolder including a plurality of blow molds arranged in a continuingseries for receiving said individual plastic container preforms insequence and blow molding said preforms into a continuing series ofplastic containers, and a common drive for coordinating continuous andsynchronous operation of said source, said cutter, said compressionmolder and said blow molder.
 2. The system set forth in claim 1 furtherincluding a preform conditioner coupled to said common drive andconnected between said compression molder and said blow molder forconditioning preforms from said compression molder preparatory to blowmolding in said blow molder.
 3. The system set forth in claim 2 furtherincluding a conveyor coupled to said common drive and connected to saidblow molder for receiving said continuing series of plastic containersfrom said blow molder.
 4. The system set forth in claim 1 wherein saidsource includes an extruder.
 5. A method of making plastic containers,which includes the steps of: (a) providing a continuous stream of moltenplastic, (b) cutting said continuous stream into individual moldcharges, (c) transferring said mold charges in sequence to a continuingseries of compression molds, (d) compression molding a continuing seriesof plastic container preforms in said compression molds, (e)transferring said continuing series of plastic container preforms insequence to a continuing series of blow molds, (f) blow molding acontinuing series of plastic containers in said blow molds, (g) removingsaid containers in sequence from said blow molds, and (h) operating saidstep (a) through (g) in synchronism to provide a continuing series ofblow molded containers from said molten plastic stream.
 6. The methodset forth in claim 5 wherein said step (e) includes conditioning saidplastic container preforms preparatory to blow molding in said step (f).7. The method set forth in claim 5 that includes at least one step,prior to said step (e) or subsequent to said step (g), selected from thegroup consisting of: crystallizing all or a portion of the finish of thepreform or container, and attaching all or a portion of a finish to thepreform or container.
 8. The method set forth in claim 5 that includesthe step of attaching a label to the container during or subsequent tosaid step (f).
 9. A system for making plastic containers, whichincludes: a source for providing a continuous stream of molten plastic,a preform molder for molding said plastic into a continuing series ofindividual plastic container preforms, a blow molder including aplurality of blow molds arranged in a continuing series for receivingsaid individual plastic container preforms in sequence and blow moldingsaid preforms into a continuing series of plastic containers, and acommon drive for coordinating continuous and synchronous operation ofsaid source, said preform molder and said blow molder.
 10. A method ofmaking plastic containers, which includes the steps of: (a) providing acontinuous stream of molten plastic, (b) molding a continuing series ofplastic container preforms, (c) transferring said continuing series ofplastic container preforms in sequence to a continuing series of blowmolds, (d) blow molding a continuing series of plastic containers insaid blow molds, (e) removing said containers in sequence from said blowmolds, and (f) operating said step (a) through (e) in synchronism toprovide a continuing series of blow molded containers from said moltenplastic stream.